EP3883720B1 - Method for laser processing, and laser machining system for carrying out the method - Google Patents

Description

The present disclosure relates to a method for laser processing a workpiece according to the preamble of claim 1 and a laser processing system according to the preamble of claim 14 for carrying out the method.

State of the art

In a device for material processing using a laser, for example in a laser processing head for laser cutting, the laser beam emerging from a laser light source or one end of a laser guide fiber is focused or bundled onto the workpiece to be processed using beam guidance and focusing optics. A laser processing head with collimator optics and focusing optics is used as standard, with the laser light being supplied via an optical fiber, also known as a laser source.

As part of laser material processing, the laser beam can be inserted into the workpiece. The piercing process precedes the actual cutting process in laser cutting. This process creates an initial hole in the workpiece that serves as the starting point for the cutting process. The duration of the grooving process is a critical factor for the efficiency of the machining process. To improve the piercing process, for example, is from the publication DE 11 2014 006 885 T5 a laser processing method for forming a puncture by irradiating a workpiece with a laser beam and cutting the workpiece starting from the puncture is known. The method includes a first piercing process to form the puncture as a blind hole extending from an upper surface to a central region of the workpiece, a cooling process for cooling the workpiece, a second piercing process to pierce the puncture to a lower surface of the workpiece, and a cutting process for cutting the workpiece. However, the process efficiency is not optimal because the duration of the piercing process and thus the process efficiency depend, for example, on the properties of the workpiece. In particular can Workpieces of the same type have manufacturing tolerances that influence the duration of the grooving process and thus the process efficiency.

EP 1 977 850 A1 shows a processing device with at least one processing head, which is designed to provide at least one high-energy processing beam, in particular an electron or laser beam.

WO 2015/039741 A1 describes a method for measuring the penetration depth of a laser beam into a workpiece, wherein the laser beam is focused in a focal spot using focusing optics arranged in a processing head.

EP 2 479 533 A1 shows a laser system to measure the change in laser melting depth in real time.

DE 10 2013 225 108 A1 shows a measuring method in which a measuring beam is emitted during machining of a workpiece using a machining beam, directed to a machining location and then evaluated using interferometry.

Disclosure of the invention

It is an object of the present disclosure to provide a method for laser machining and a laser machining system for carrying out the method, which can improve efficiency of a piercing operation. In particular, it is an object of the present disclosure to shorten a time for a piercing process into a workpiece that precedes a cutting process.

This object is achieved by a method according to claim 1 and by a laser processing system according to claim 14. Advantageous embodiments of the invention are specified in the subclaims.

The method includes: piercing a piercing hole into a workpiece using a laser beam, measuring a piercing depth of the piercing hole using at least one optical measuring beam during the piercing process and adjusting at least one process parameter of the laser processing system during the piercing process based on a currently measured piercing depth. The method may implement the aspects of the apparatus for a laser processing system according to the present disclosure.

A device for a laser processing system, in particular a laser cutting head, comprises an optical measuring device, which is set up to determine a current or instantaneous piercing depth of a piercing hole created with a laser beam in a workpiece during a piercing process using at least one optical measuring beam, and a control device , which is set up to adjust at least one process parameter of the laser processing system during the piercing process based on the current piercing depth.

According to the invention, the piercing depth can be known at any time during the piercing process. The at least one process parameter of the laser processing system can be specifically set or regulated based on the current piercing depth. This allows for inline control of the piercing process (and, for example, puncture detection), whereby the duration of the piercing process can be minimized, the quality of the piercing hole can be optimized and/or process stability can be maximized. For example, the quality of the piercing hole can be determined by the amount and extent of the material deposited on the top of the workpiece and/or by the diameter of the piercing hole along the direction of propagation. Through inline control, one or more process parameters can be controlled in this way can be adjusted so that the amount and the extent of the material throw-up and/or the diameter of the piercing hole meet predetermined quality criteria.

Preferably, the optical measuring device is set up to continuously or continuously measure the piercing depth during the piercing process. The control device can be set up to continuously or continuously adjust or regulate the at least one process parameter based on the continuously measured piercing depth during the piercing process. Here, a time-resolved continuous measurement of the piercing depth can take place over a period of time or over the entire duration of the piercing process. Likewise, the at least one process parameter can be adjusted or regulated accordingly over the period of time or over the entire duration of the piercing process.

The device, such as the optical measuring device or the control device, is set up to determine a rate of change ds / dt of the piercing depth s (t), i.e. a change in the piercing depth. The control device is set up to set the at least one process parameter based on the rate of change ds / dt of the piercing depth s(t) . By determining or recording the rate of change ds / dt , the efficiency of the piercing process can be analyzed, for example with regard to the current material output.

The duration of the piercing process, which may be defined as the time between activation of the laser beam and piercing through the workpiece, may depend on the rate of change ds / dt of the piercing depth. For example, the rate of change ds / dt of the piercing depth s(t) can decrease as the depth of the piercing hole increases. This can be due to the decreasing intensity of the laser beam that can be coupled to the base of the puncture as the puncture depth s(t) increases. Furthermore, the rate of change ds / dt of the piercing depth s(t) can directly reflect the process efficiency. According to the present invention, the current piercing depth s(t) and also the rate of change ds / dt are known at any time during the piercing process, whereby one or more process parameters of the laser processing system can be adjusted and regulated in a more targeted manner.

Preferably, the control device is further set up to compare the rate of change ds / dt of the piercing depth s(t) with a (for example predetermined) threshold value, and to determine based on the comparison whether piercing the workpiece is possible with the currently set process parameters or not. The threshold value can in particular indicate when material penetration is no longer possible with the current process parameters.

In some embodiments, the control device can be set up to abort the piercing process or to set the at least one process parameter to at least a predefined value if it is determined that piercing the workpiece is not possible with the currently set process parameters. If the rate of change ds / dt reaches the defined threshold value, a control algorithm that is designed for this case can be used, for example. Alternatively, the piercing process can be aborted and/or an error message can be issued to the operator. After the piercing process has been aborted, the piercing process can be automatically restarted at a different position on the workpiece.

Preferably, the device is further set up to detect piercing of the laser beam through the workpiece. For example, piercing can be detected when the optical measuring device no longer receives an optical measuring beam reflected from the bottom of the puncture hole. Piercing can also be determined or detected based on the rate of change ds / dt .

The control device is preferably set up to carry out a laser cutting process on the workpiece after the piercing has been detected. For example, the time of piercing can be communicated to the control unit and the subsequent cutting process can be started directly and without delay. For the cutting process, the laser cutting head can be moved along the workpiece to form a cutting contour.

Preferably, the control device is set up to determine a thickness or material thickness of the workpiece based on a piercing depth at a time when the laser beam penetrates the workpiece. This information can for example, communicated to the control unit. Based on this, the control unit can automatically select the correct process parameters, which can be dependent on material thickness, for example, for the subsequent cutting process. Additionally or alternatively, the information can be used to carry out a (for example automated) comparison between the target material thickness and the actual material thickness. If there is a deviation, an error message can be sent to the machine operator or the machine control, for example, in order to be able to react to the deviation in material thickness at an early stage.

Preferably, the control device is set up to adjust the at least one process parameter discretely, continuously, or in combination discretely and continuously during the piercing process. For example, several value ranges can be defined for the piercing depth or rate of change ds / dt , with each of the several value ranges being assigned a respective discrete process parameter. In a further example, the at least one process parameter can be adjusted continuously depending on the current piercing depth or rate of change ds / dt . In yet another example, a combined discrete and continuous adjustment may occur over the duration of the piercing process. For example, a discrete adjustment can be made for at least a first range of values of the penetration depth or rate of change ds / dt and a continuous adjustment can be made for at least a second range of values of the penetration depth or rate of change ds / dt, which is different from the at least one first range of values.

Preferably, the at least one process parameter of the laser processing system is selected from the group that includes at least one pulse parameter, a laser power, a focus position of the laser beam, a focus diameter of the laser beam, a process gas composition, a process gas pressure and a nozzle distance between a nozzle of the laser processing system and a surface of the workpiece . The at least one pulse parameter can be selected from the group that includes a pulse length, a pulse period and a pulse peak power. Further pulse parameters can result from the pulse parameters mentioned.

When cutting metallic materials using laser radiation, a process gas can usually flow from the cutting head together with the laser beam Workpiece can be aligned. For this purpose, a cutting nozzle can be attached to a laser processing head of the laser processing system, through which laser radiation and process gas are directed onto a workpiece to be processed. The process gas can be an inert medium (eg nitrogen N ₂ ) or a reactive gas (eg oxygen Oz). The at least one process parameter can include a composition of the process gas and/or a pressure of the process gas. By specifically adjusting the composition and/or the pressure of the process gas, the quality of the piercing process can be improved and the duration of the piercing process can be reduced.

The optical measuring device preferably comprises or is a coherence interferometer, and in particular a short coherence interferometer. The coherence interferometer (optical coherence tomography, OCT) can be used to measure various process parameters, such as the penetration depth during the piercing process, the distance to the workpiece during laser cutting and/or a surface topography.

Preferably, the device is set up to carry out the piercing process at a substantially constant distance between the laser processing head or a nozzle of the laser processing system and a surface of the workpiece. The nozzle can be a cutting nozzle from which the laser beam and optionally a process gas emerge. The optical measuring device can be set up to determine the current piercing depth based on the distance and a current measured value at the piercing position. The distance can include an initial measurement value determined before the start of the piercing process. The optical measuring device can be set up to determine the initial measured value. For example, before the start of the piercing process, the optical measuring device can carry out a calibration measurement (e.g. a distance measurement with the coherence interferometer) to determine the initial measurement value, as soon as the cutting optics have reached their XYZ end position for the piercing process. Alternatively, the distance between the laser processing head or. the nozzle and the workpiece surface can be known or can be determined based on an actuating signal from the control unit for adjusting the distance. Using the distance and the current measurement signal during the The current piercing depth s(t) can be determined. The current measurement signal can, for example, include a reflection of the optical measurement beam at the piercing position. The optical measuring device can be set up to convert the current measurement signal into a current measured value. The current measured value can correspond to a distance at the piercing position.

Preferably, the device is alternatively or additionally set up to carry out the piercing process at a time-changing distance between the laser processing head or the nozzle of the laser processing system and the surface of the workpiece. In other words, the distance can be varied during the piercing process, for example dynamically. The current piercing depth can be determined based on a current distance with respect to the workpiece surface and a corresponding current measured value of the optical measuring device at the piercing position. In other words, the current distance and the corresponding current measured value can be determined at the same time. The current distance can either be measured or determined based on a current control value for setting the current nozzle distance. For example, the optical measuring device can be set up to determine the current distance.

In one embodiment, in addition to the optical measuring device, which includes, for example, a short coherence interferometer, a distance sensor unit can be used which measures the distance between the nozzle tip and the top of the workpiece, for example capacitively, inductively, optically or in another way. Both measurement signals, i.e. the nozzle distance signal from the distance sensor unit and the corresponding measurement signal from the optical measuring device, are communicated, for example, to the control unit, which in turn can determine the current or momentary penetration depth, for example mathematically.

Alternatively or additionally, the optical measuring device can be set up to direct a first optical measuring beam to a piercing position and a second optical measuring beam to the surface of the workpiece. The device can then be set up to determine the current puncture depth by means of a first reflection of the first optical measuring beam at a puncture base of the puncture hole and a second reflection of the second optical measuring beam. For example, the optical measuring device include at least one optical element which is set up to divide the optical measuring beam into two partial beams. The first partial beam can be directed at the piercing position or the piercing base. The second partial beam can be directed, for example, onto the top of the workpiece as a further reference value. Both partial beams can be superimposed on each other or with a beam from a reference arm of the optical measuring device in order to determine the absolute current penetration depth. This is applicable for both a constant and a variable nozzle distance to the workpiece surface.

Preferably, the optical measuring device is set up to guide the at least one optical measuring steel over the surface of the workpiece in at least one direction perpendicular to an axis of the optical measuring beam. The optical measuring device can be set up to scan the surface of the workpiece in two mutually perpendicular directions with the at least one optical measuring steel. In other words, dynamic measuring spot positioning can take place. Preferably, the optical measuring device is set up to carry out a topography measurement of the surface of the workpiece using the at least one optical measuring steel. For this purpose, the optical measuring device can determine measurement data, such as height data or distance data, at the piercing position and an area of the workpiece surface surrounding the piercing position.

In particular, the device can be set up to carry out a geometric characterization of the puncture hole. The geometric characterization may include two-dimensional or three-dimensional characterization. The two-dimensional characterization can, for example, record a diameter of the piercing hole or an extent of material adhesions and build-ups around the piercing hole. The three-dimensional characterization can also contain height data or height information, for example a height of the material adhesions or throws, a hole depth or topography of the surface around and at the puncture hole. The geometric characterization of the piercing hole can directly reflect the quality (e.g. diameter on the entry side, material adhesions, material build-up, etc.) of the piercing process or the piercing hole. The geometric characterization makes it possible, for example, to make a statement about the diameter of the puncture hole Entry side (top of the workpiece). Knowing the diameter in turn enables a target/actual comparison between the diameter and the expected cutting gap width, which can be determined, for example, through previous tests. A determination of the diameter and/or a comparison of the diameter of the piercing hole with a predetermined value can be carried out between the actual piercing and the contour cut. If the diameter of the piercing hole is smaller than the expected cutting gap width of the contour or is the same size, the piercing process can take place directly on the contour. This means that if the diameter of the piercing hole is smaller than or equal to the expected cutting gap width of the contour, the contour cutting can begin directly at the piercing position.

Preferably, the optical measuring device dynamically guides the at least one optical measuring steel over the surface of the workpiece during the piercing process and/or after the piercing process. In other words, the geometric characterization can take place during (in-process/inline) and/or after (post-process) the piercing process into the workpiece.

Preferably, the control device is set up to set at least one process parameter for a subsequent piercing process based on the geometric characterization of the piercing hole. In particular, the geometric characterization of the piercing hole enables the optimization of subsequent piercing processes in order to improve the quality of the piercing holes of the subsequent piercing processes by adapting the process parameters, for example based on a self-learning system (machine learning). Additionally or alternatively, the quality information can be communicated to the machine operator, for example using an HMI interface. This gives the operator the opportunity to intervene in the ongoing process if necessary and to take corrective measures such as jet centering, checking the nozzle for damage or similar.

Preferably, the device, and in particular the optical measuring device or the control device, is set up to determine a diameter of the puncture hole. The control device can be set up to compare the diameter with a (eg predetermined) threshold value. The control device can control the laser processing system after piercing the laser beam through the workpiece and before starting a cutting operation such that the laser beam increases the diameter of the piercing hole when it is determined that the diameter is equal to or smaller than the threshold value. By knowing the diameter, for example, it can be geometrically evaluated whether there is a piercing hole that can be cut or not. If necessary, the piercing hole can be specifically enlarged to a target diameter at the beam entry point and along the piercing hole before the actual cutting process in order to promote the coupling of energy for the cutting process. This can increase process reliability.

According to a further aspect of the present invention, a laser processing system according to claim 14 is specified. The laser machining system includes a machining head with a laser device that is set up to direct the laser beam onto a machining area of a workpiece, and the device described above.

The laser processing head can have one or more optical elements. All optical elements of the laser processing head can be reflective optics. Alternatively, all optical elements of the laser processing head can be transmissive optics or the optical elements can include both transmissive and reflective optics. The laser processing head preferably comprises at least one optical element which is displaceable with respect to an optical axis in order to adjust a focus position of the laser beam and/or a focus position of the at least one optical measuring beam. The at least one optical element can include transmissive and/or reflective optics, and can include or be, for example, a lens, a lens group, a zoom optics, a mirror optics or the like. The at least one optical element can be selected from the group that includes or consists of a collimator optics for the laser beam, a collimator optics for the at least one optical measuring beam and a focusing optics. The focusing optics can be a common focusing optics for the laser beam and the at least one optical measuring beam. These optics can be or include a lens or a lens group.

Preferably, the laser processing system is set up for processing workpieces with a thickness of at least 10mm, and in particular at least 15mm. The embodiments of the present disclosure can be used for all material thicknesses, and are particularly advantageous for grooving in larger material thicknesses (≥ 10 mm). For larger material thicknesses, the piercing process can take several seconds, for example, and can therefore take up a large amount of time in the actual cutting process. By shortening the duration of the grooving process, the overall duration of the machining process can be reduced and thus the process efficiency can be increased.

Brief description of the drawings

• Figur 1 ein Laserbearbeitungssystem gemäß Ausführungsformen der vorliegender Erfindung,
• Figur 2 ein Laserbearbeitungssystem gemäß weiteren Ausführungsformen der vorliegender Erfindung,
• Figur 3 ein Laserbearbeitungssystem gemäß weiteren Ausführungsformen der vorliegenden Erfindung,
• Figur 4 ein Laserbearbeitungssystem gemäß weiteren Ausführungsformen der vorliegenden Erfindung,
• Figur 5 ein Laserbearbeitungssystem gemäß weiteren Ausführungsformen der vorliegenden Erfindung,
• Figuren 6A und B schematische Darstellung des Einstechprozesses und der Bestimmung einer Einstechtiefe gemäß Beispielen, die nicht Gegenstand der Erfindung sind,
• Figur 7(a) bis 7(c) qualitative Verläufe einer Einstechtiefe und von Änderungsraten einer Einstechtiefe gemäß Ausführungsformen der vorliegenden Erfindung,
• Figur 8 qualitative Verläufe von Prozessparametern des Laserbearbeitungssystems gemäß Ausführungsformen der vorliegenden Erfindung, und
• Figur 9(a) und 9(b) Messfleckpositionierungen für eine geometrische Charakterisierung gemäß Ausführungsformen der vorliegenden Erfindung.

Embodiments of the disclosure are shown in the figures and are described in more detail below. Show it:

• Figure 1 a laser processing system according to embodiments of the present invention,
• Figure 2 a laser processing system according to further embodiments of the present invention,
• Figure 3 a laser processing system according to further embodiments of the present invention,
• Figure 4 a laser processing system according to further embodiments of the present invention,
• Figure 5 a laser processing system according to further embodiments of the present invention,
• Figures 6A and B schematic representation of the piercing process and the determination of a piercing depth according to examples that are not the subject of the invention,
• Figures 7(a) to 7(c) qualitative curves of a puncture depth and of rates of change of a puncture depth according to embodiments of the present invention,
• Figure 8 qualitative curves of process parameters of the laser processing system according to embodiments of the present invention, and
• Figures 9(a) and 9(b) Measuring spot positioning for geometric characterization according to embodiments of the present invention.

Embodiments of the invention

In the following, unless otherwise noted, the same reference numerals are used for elements that are the same and have the same effect.

Figure 1 shows a schematic representation of a laser processing system 100 according to embodiments of the present invention. The laser processing system 100 may include a laser cutting head 101.

The laser processing system 100 includes a laser device 110 for providing a laser beam 10 (also called a “processing beam” or “processing laser beam”) and the device according to the embodiments described here. The device comprises an optical measuring device 200, which is set up to determine a piercing depth of a piercing hole 2 created with the laser beam 10 in a workpiece 1 during a piercing process using at least one optical measuring beam 13. The device further comprises a control device 300, which is set up to adjust at least one process parameter of the laser processing system 100 during the piercing process based on a currently measured piercing depth.

The laser device 110, which can be controlled by a laser control device 115, is set up to direct the laser beam 10 onto a processing area of the workpiece 1. The laser device 110 may have a collimator lens 120 for collimating the laser beam 10. Within the laser welding head 101, the laser beam 10 is deflected by approximately 90° in the direction of the workpiece 1 by suitable optics, such as a beam deflector 130.

In some embodiments, the laser beam 10 and the at least one optical measuring beam 13 can be coaxial at least in some areas, and in particular can be superimposed coaxially at least in some areas. For example, the laser beam 10 and the at least one optical measuring beam 13 can be guided essentially coaxially through the cutting optics into the processing zone by the beam deflector 130. The combination of the optical measuring beam 13 and the laser beam 10 can take place after the collimator optics 210 and in front of a focusing optics 220. The beam deflector 130 is preferably reflective for the wavelength of the laser beam 10 and transmitting for the wavelength of the at least one optical measuring beam 13.

The optical measuring device 200 can comprise a coherence interferometer or a coherence tomograph or can be a coherence interferometer or a coherence tomograph. The coherence tomograph typically includes a collimator optics 210, which is set up to collimate the at least one optical measuring beam 13, and the focusing optics 220, which is set up to focus the at least one optical measuring beam 13 onto the workpiece 1. The focusing optics 220 can be a common focusing optics, such as a focus lens, for the laser beam 10 and the at least one optical measuring beam 13.

In typical embodiments, the collimator optics 210 and the focusing optics 220 are integrated into the cutting head 101. For example, the cutting head 101 may include a collimator module that is integrated into the cutting head 101 or mounted on the cutting head 101.

The principle described here for measuring the penetration depth can be based on the principle of optical coherence tomography, which makes use of the coherence properties of light with the aid of an interferometer. The coherence tomograph can include an evaluation unit 240 with a broadband light source (e.g. a superluminescent diode, SLD), which couples the measuring light into an optical waveguide 242. In a beam splitter 244, which preferably has a fiber coupler, the measuring light is split into a reference arm 246 and a measuring arm, which leads into the cutting head 101 via an optical waveguide 248.

The collimator optics 210 serves to collimate the measuring light (optical measuring beam 13) emerging from the optical waveguide 248. According to some embodiments, the at least one optical measuring beam 13 in the cutting head 101 can be coaxially superimposed on the laser beam 10. Subsequently, the laser beam 10 and the at least one optical measuring beam 13 can be focused on the workpiece 1 by the focusing optics 220, which can be a common lens or focusing lens.

The at least one optical measuring beam 13 can be directed into the piercing hole in the workpiece 1. The measuring light reflected back from the puncture hole, and in particular from the bottom of the puncture hole, is imaged by the focusing optics 220 onto the exit/entrance surface of the optical waveguide 248, superimposed in the fiber coupler 244 with the back-reflected light from the reference arm 246 and then back into the evaluation unit 240 directed. The superimposed light contains information about the path length difference between the reference arm 246 and the measuring arm. This information is evaluated in the evaluation unit 240 based on coherence interferometry or short coherence interferometry, whereby the User receives information about the distance between the bottom of the piercing hole and a reference, for example the cutting head 101. The determination of the penetration depth is later with reference to Figures 6A and B explained in more detail.

In order to be able to measure the entire penetration depth, especially in the thick material area, inline, i.e. in real time, in some embodiments the measuring range of the interferometer is tracked during the penetration process. For this purpose, for example, the length of the reference arm 246 can be moved or adjusted dynamically. Alternatively, the reference arm 246 may include multiple reference levels corresponding to the different measurement ranges.

The laser processing system 100 can comprise at least one optical element for the laser beam 10 and/or for the at least one optical measuring beam 13, which is set up to adjust the focus position of the laser beam 10 or the at least one optical measuring beam 13. The at least one optical element can be displaceable along the optical axes in the diverging region of the respective beam in order to change the focus positions. In the Figure 1 For example, the collimator lens 120 and the collimator optics 210 are shown as being displaceable along the respective optical axis. Here, the focus positions of the laser beam 10 and the at least one optical measuring beam 13 can be changed together or independently of one another.

The adjustment/displacement of the optical elements with respect to the optical axis to change the focus position of both beams can be done by motor, manually or by a combination of motor and manual. For example, the focus position of the laser beam 10 can be adjusted by motor and the focus position of the at least one optical measuring beam 13 can be adjusted manually.

The control device 300 is set up to adjust at least one process parameter of the laser processing system 100 during the piercing process based on a piercing depth currently measured by the optical measuring device 200. The control device 300 can communicate with at least one of the laser device, the laser optics, the laser source and the measuring system in order to be able to regulate the piercing process. The control device 300 can, for example, with the Laser control device 115 may be connected to set a pulse parameter and / or a laser power of the laser device 110. Additionally or alternatively, the control device 300 can be connected to laser optics of the processing head 101, for example to set a focus position and/or a focus diameter of the laser beam 10. In particular, the control device 300 can issue control commands for moving the collimator lens 120 and/or the collimator optics 210 along the respective optical axis.

The laser processing system 100 or parts thereof, such as the cutting head 101, can be movable along a processing direction 20 according to embodiments. The processing direction 20 can be a cutting direction with respect to the workpiece 1. In particular, the processing direction 20 can be a horizontal direction. The processing direction 20 can also be referred to as the “feed direction”.

The laser processing system 100, and in particular the cutting head 101, cannot be moved along the processing direction 20 during the piercing process. In other words, the laser processing system 100, and in particular the cutting head 101, can remain in the same location in an xy plane. However, during the piercing process, the cutting head 101 can be moved in the (eg vertical) z direction in order to set a nozzle distance between a nozzle of the laser processing system (not shown) and the surface 3 of the workpiece 1. Figure 2 shows a laser processing system according to further embodiments of the present invention. The laser processing system Figure 2 is similar to referring to the Figure 1 Laser processing system described and a description of similar or identical elements will not be repeated. In the example of Figure 2 is the at least one optical element that is set up to adjust the focus position of the laser beam 10 or the at least one optical measuring beam 13, the focusing optics 220. In particular, the at least one optical element can be in the collimated area of the superimposed beams along the optical axis be movable. This means that the focus position of both beams can be changed at the same time.

Figure 3 shows a laser processing system according to further embodiments of the present invention. The laser processing system Figure 3 is similar to referring to the Figure 1 Laser processing system described and a description of similar or identical elements will not be repeated. In the example of Figure 3 This includes at least one optical element, which is set up to adjust the focus position of the laser beam 10 or the at least one optical measuring beam 13, the collimator optics 210 and the focusing optics 220. In particular, at least one displaceable optical element can be in the diverging area of the at least one measuring beam 13 and at least one further displaceable optical element can be present in the collimated area of both beams. This allows the focus positions of the beams to be changed independently of each other. Figure 4 shows a laser processing system according to further embodiments of the present invention. The laser processing system Figure 4 is similar to referring to the Figure 1 Laser processing system described and a description of similar or identical elements will not be repeated.

In example the Figure 4 the laser beam 10 is coaxial to the cutting optics and the at least one optical measuring beam 13 is coupled in laterally. For example, the beam deflector 130 can be transmissive for the laser beam 10 and reflective for the at least one optical measuring beam 13. In this case too, all of the previously described combinations for changing the focus position are possible.

Figure 5 shows a laser processing system according to further embodiments of the present invention. The laser processing system Figure 5 is similar to referring to the Figure 1 Laser processing system described and a description of similar or identical elements will not be repeated.

The laser processing system or the device additionally has a deflection system 500 in the measuring beam path, which is set up to scan an area of the workpiece surface with the at least one optical measuring beam 13. The area of the workpiece surface can include the piercing position or the processing position to which the laser beam is directed, as well as an area surrounding this position. The at least one optical measuring beam 13 can thus be dynamic and be positioned on the workpiece 1 independently of the laser beam 10. The deflection system 500 can, for example, have at least one reflecting mirror 510 that is movable about at least one axis. The mirror 510 is preferably movable about two mutually perpendicular axes. The deflection system 500 can in particular be a scanner system. In Figure 5 Two movable mirrors 510 are shown, which can be rotated about two different mutually perpendicular axes Figure 9 is shown. For dynamic measuring spot positioning, further embodiments are possible, which include, for example, transmitting optical elements or involve moving the fiber end of the measuring beam.

Figures 6A and B show the determination of a penetration depth s(t) according to an example that is not the subject of the invention.

The current penetration depth s(t) can be determined in various ways using the at least one optical measuring beam 13. Three options are discussed below. However, the present disclosure is not limited to this and other suitable methods for determining a penetration depth s(t) may be used.

In a first option, with reference to the Figure 6A , the nozzle distance d(t) between a nozzle 103 of the laser processing system and a surface 3 of the workpiece is essentially constant ( d(t) = const .). The current piercing depth can be determined based on an initial measurement value determined before the start of the piercing process and a current measurement value. For example, before piercing begins, a calibration measurement is carried out (e.g. a distance measurement with the interferometer). Alternatively, the initial measurement value can be determined based on a control value for the initial position of the laser processing head or transmitted by a control unit. From the measurement signal, which can be based on a reflection of the optical measuring beam, the optical measuring device 200 or the control device 300 can determine a measured value corresponding to a distance between the nozzle 103 and a bottom of the puncture hole. With the initial measurement value and the measurement signal at the position of the piercing hole, the current piercing depth s(t) can be determined during piercing.

In a second option, again referring to the Figure 6A , the nozzle distance d(t) between the nozzle 103 of the laser processing system and the surface 3 of the workpiece changes during the piercing process ( d(t)≠const. ) . In other words, the nozzle distance d(t) is variable. In addition to the optical measuring system, a distance sensor unit can be used which measures the distance between the nozzle 103 and the workpiece top 3, for example capacitively, inductively or optically. Both measurement signals, i.e. the nozzle distance signal from the distance sensor unit and the measurement signal from the optical measuring system 200, are communicated to the higher-level control unit 300, which in turn can mathematically determine the current penetration depth. In a third option, with reference to the Figure 6B , the nozzle distance d(t) between the nozzle 103 of the laser processing system and the surface 3 of the workpiece also changes during the piercing process ( d(t)≠const. ) . The at least one measuring beam includes a first measuring beam 13a and a second measuring beam 13b. For example, an initial measuring beam in the measuring arm can be divided into two partial beams using at least one optical element. The first partial beam 13a is directed onto the puncture base or the bottom of the puncture hole. The second partial beam 13b is directed, for example, at the workpiece surface 3 as a reference value. Both partial beams 13a and 13b are superimposed on each other and/or with a beam from a reference arm. The partial beams 13a and 13b can hit the workpiece at an angle to each other, as in Figure 6B shown, or parallel and spaced apart from each other. Alternatively, the optical measuring beam can have such a large diameter that the measuring beam can be directed both onto the workpiece surface 3 and onto the piercing base. The absolute current piercing depth s(t) can in turn be determined from both measurement signals from the workpiece surface 3 and the piercing base.

Figure 7 shows a piercing depth s(t) and rates of change ds / dt of a piercing depth s(t) according to embodiments of the present invention.

In Figure 7(a) the penetration depth s(t) is shown as a function of time t . When a certain penetration depth s(t) is reached, the piercing takes place. The puncture can be recognized, for example, by the fact that no measurement signal or reflection of the measurement beam is no longer received. From the penetration depth s(t) when piercing can be: For example, the thickness or material thickness of the workpiece can be derived. In particular, the piercing depth s(t) can correspond to the thickness or material thickness of the workpiece when piercing. After the piercing has been detected, a laser cutting process, such as a contour cut, can be carried out on the workpiece.

In Figure 7(b) a rate of change ds / dt of the piercing depth s(t) is shown as a function of time t . When the puncture occurs, the rate of change ds / dt drops to zero or is no longer determinable. This is the case, for example, if the optical measuring device no longer receives a measuring beam reflected from the puncture base, from which the puncture can be recognized.

In Figure 7(c) a rate of change ds / dt of the piercing depth s(t) is shown as a function of time t . Above a specified threshold value, material penetration is not possible with the current process parameters. If this threshold value is reached or fallen short of during piercing, the piercing process can be aborted and/or an error message can be issued to the operator.

Figure 8 shows process parameters of the laser processing system according to embodiments of the present invention.

According to the present disclosure, the current penetration depth s(t) is known at every time t . Based on the current piercing depth s(t), at least one process parameter of the piercing process is controlled inline. In Figure 8 qualitative curves of different process parameters are shown depending on the current piercing depth s(t) .

The at least one process parameter of the laser processing system can, for example, be selected from the group that includes at least one pulse parameter, a laser power, a focus position of the laser beam, a focus diameter of the laser beam, a process gas composition, a process gas pressure and a nozzle distance between a nozzle of the laser processing system and a surface of the Workpiece includes.

One, two or more process parameters can be set during the piercing process. The parameter curves can be more discrete, more continuous or be of mixed nature. The parameter curves can increase or decrease as the penetration depth increases. In the example of Figure 8 process parameter 1 changes discretely, process parameter 2 changes continuously and process parameter 3 combines discrete and continuous. The process parameters can also be set discretely, continuously or partly discretely and partly continuously.

With regard to the exemplary process parameter 1, several value ranges can be defined for the piercing depth s(t) and the rate of change, with each of the several value ranges being assigned a respective discrete process parameter.

Regarding the exemplary process parameter 2, this is adjusted continuously depending on the current piercing depth and the rate of change. For example, the process parameter can continuously increase or decrease as the penetration depth increases.

With regard to the exemplary process parameter 3, a combined discrete and continuous setting takes place over the duration of the piercing process. For example, a discrete adjustment can be made for at least a first value range of the penetration depth and the rate of change and a continuous adjustment can be made for at least a second value range of the penetration depth and the rate of change, which is different from the at least one first value range.

Figure 9 shows measurement spot positioning for geometric characterization according to embodiments of the present invention. In Figure 9(a) A dynamic 2D measuring spot positioning "in-process" (left) and "post-process" (right) is shown. In Figure 9(b) 1D measuring spot positioning (left) and 2D measuring spot positioning/cross scan (right) are shown. “Measuring spot” here refers to the point of the measuring beam on the workpiece 2, at which the measuring beam is reflected in order to obtain a measuring signal.

In some embodiments, a geometric characterization or topography measurement of the puncture hole is carried out, which, for example, reflects the diameter of the puncture hole and material adhesions or build-ups 5 of the puncture process on the entry side. For this purpose, the optical measuring device Measured values, ie height data, are determined at the position of the puncture hole and in an area surrounding it. The geometric characterization can take place during (“in-process” or “inline”) or after (“post-process”) the piercing process, as in the example of Figure 9(a) is shown. For this purpose, dynamic measuring spot positioning, for example scanning the workpiece surface 3 using the measuring beam in at least one direction, preferably in two mutually perpendicular directions X and Y, can be used.

For the measuring spot positioning, the measuring spot 13 can be used by a deflection unit, as shown for example in the Figure 5 is shown, can be moved or positioned in-process. For this purpose, the deflection unit can comprise at least one mirror, which is movable or pivotable about at least one axis perpendicular to the beam axis of the measuring beam. In another example, the measuring spot 13 can be moved or positioned relative to the workpiece by horizontally moving the laser processing optics in the XY plane and/or by horizontally moving the workpiece in the XY plane relative to the laser processing optics after the piercing process (post-process). . In other words, the laser processing optics can be shifted perpendicular to an optical axis of the optics or perpendicular to the beam axis of the measuring beam in order to scan the workpiece surface 3 with the measuring beam or measuring spot 13. For example, collimation optics can be moved in the beam path of the measuring beam in order to move the measuring beam accordingly.

Referring to the Figure 9(b) the measuring spot 13 is positioned to characterize the puncture hole 2 and optionally the material projection 5 starting from the center of the puncture hole 2 in at least one spatial direction X perpendicular to the beam axis of the measuring beam or parallel to the workpiece surface 3 (left in Figure 9(b) ). Another example is a cross scan in two mutually perpendicular directions (XY direction) starting from the center of the puncture hole 2 (left in Figure 9(b) ).

In both options, a correspondingly large number of measuring points is preferably used in order to achieve sufficient resolution of the geometric (in particular the three-dimensional) shape of the puncture hole and/or the material adhesions and material build-ups 5. In addition, further scanning strategies are available Measuring spot 13 possible, for example spirally around the center of the puncture hole 2, in the shape of an 8, etc.

According to the invention, an optical measuring device, in particular a short coherence interferometer, is used for the temporal resolution of the piercing depth in the piercing process. The piercing depth can therefore be known at any time during the piercing process. The at least one process parameter of the laser processing system is specifically set or regulated based on the current piercing depth. This results in inline control of the piercing process (and e.g. puncture detection), whereby the duration of the piercing process can be minimized, the quality of the piercing hole can be optimized and/or process stability can be maximized. For example, the quality of the piercing hole can be determined by the amount and extent of the material deposited on the workpiece surface and/or by the diameter of the piercing hole along the direction of propagation. Through the inline control, one or more process parameters can be set in such a way that the amount and extent of the material throw-up and/or the diameter of the piercing hole meet predetermined quality criteria.

Claims (15)

1. A method for laser machining a workpiece (1), in particular for laser cutting a workpiece (1), with a laser machining system (100), comprising:

   piercing a piercing hole (2) into the workpiece (1) with a laser beam (10);

   measuring a current piercing depth of the piercing hole (2) by at least one optical measuring beam (13) during the piercing operation; and

   adjusting at least one process parameter of the laser machining system (100) during the piercing operation based on the current piercing depth to control and/or regulate the piercing operation,

   characterised in that a rate of change of the piercing depth is determined and the at least one process parameter is adjusted based on the rate of change.
2. The method according to claim 1, wherein the rate of change of the piercing depth is compared with a threshold value and, based on the comparison, it is determined whether piercing through the workpiece (1) is possible or not; and/or
   wherein the at least one process parameter is adjusted discretely, continuously, or combined discretely and continuously during the piercing operation.
3. The method according to any one of the preceding claims, wherein the at least one process parameter of the laser machining system (100) comprises at least one of or is one of the following parameters:
   a pulse parameter, a pulse length, a pulse period duration, a pulse peak power, a laser power, a focus position of the laser beam (10), a focus diameter of the laser beam (10), a process gas composition, a process gas pressure, and a distance between a laser machining head (101) and a surface (3) of the workpiece (1).
4. The method according to any one of the preceding claims, wherein the piercing depth is determined based on a reflection of the optical measuring beam (13) from a piercing bottom of the piercing hole (2), and wherein a piercing through of the laser beam (10) through the workpiece (1) is detected based on that no reflection from the piercing bottom is obtained any longer, and wherein after detecting the piercing through, a laser machining operation is carried out on the workpiece (1); and/or
   wherein a thickness of the workpiece (1) is determined based on a most recent detected piercing depth before piercing through of the laser beam (10) through the workpiece (1).
5. The method according to any one of the preceding claims, wherein, with a substantially constant given distance between the laser machining system (100), in particular a laser machining head (101) of the laser machining system (100), and a surface (3) of the workpiece (1) during the piercing operation, the current piercing depth is determined based on the given distance and a current measured value.
6. The method according to any one of the preceding claims, in which, with a time-varying distance between the laser machining system (100), in particular a laser machining head (101) of the laser machining system (100), and a surface (3) of the workpiece (1) during the piercing operation, the current piercing depth is determined based on a current distance and a current measured value of the optical measuring device (200) from a piercing bottom of the piercing hole (2).
7. The method according to claim 6, wherein the current distance between the laser machining system (100), in particular a laser machining head (101) of the laser machining system (100), and the surface (3) of the workpiece (1) is measured capacitively, inductively and/or optically by means of a distance sensor unit.
8. The method according to any one of the preceding claims, wherein a first optical measuring beam (13a) is directed onto a piercing bottom of the piercing hole (2) and a second optical measuring beam (13b) is directed onto a surface (3) of the workpiece (1) and the current piercing depth is determined by means of the first optical measuring beam (13a) and the second optical measuring beam (13b).
9. The method according to any one of the preceding claims, wherein during the piercing operation and/or after the piercing operation a surface (3) of the workpiece (1) is scanned with the at least one optical measuring beam (13) in at least one direction perpendicular to the beam axis of the laser beam (10) in order to carry out a geometric characterisation of the piercing hole (2).
10. The method according to claim 9, wherein, based on the geometric characterisation of the piercing hole (2), at least one process parameter of the laser machining system (100) is adjusted or stored for the subsequent machining operation or for a subsequent piercing operation.
11. The method according to one of the preceding claims 9 or 10, wherein, based on the geometric characterisation of the piercing hole (2), a diameter of the piercing hole (2) at the workpiece surface (3) and/or along an expansion direction of the piercing hole (2) is determined.
12. The method according to claim 11, wherein the laser machining system (100) is driven in order to enlarge the diameter of the piercing hole (2) with the laser beam (10) when the diameter is equal to or smaller than a threshold value.
13. The method according to any one of the preceding claims, wherein workpieces having a thickness of at least 10 mm, or of at least 15 mm are machined.
14. A laser machining system (100) for machining, in particular for cutting, a workpiece (1) by means of a laser beam (10), comprising:

    a laser machining head (101) having a laser device (110) configured to direct the laser beam (10) onto the workpiece (1) for piercing a piercing hole (2) for a subsequent machining operation; and

    an optical measuring device (200) configured to determine a current piercing depth of the piercing hole (2) during the piercing operation using at least an optical measuring beam (13); and

    a control device (300) configured to adjust at least one process parameter of the laser machining system (100) during the piercing operation based on the current piercing depth to control and/or regulate the piercing operation,

    characterised in that

    the laser machining system (100) is configured to carry out a method according to any one of the previous claims, wherein the control device (300) is configured to determine the rate of change of the piercing depth and to adjust the at least one process parameter based on the rate of change of the piercing depth.
15. The laser machining system (100) according to claim 14, wherein the optical measuring device (200) comprises or is a coherence interferometer or a short coherence interferometer.

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